Influence of deformation process on microstructure and properties of 2014 aluminium alloy

The comparisons of forging-extrusion multistage hot deformation, forging and extrusion hot deformation processes on microstructure, mechanical property and impact toughness of 2014 Al alloy have been investigated. Results showed that the strength and impact toughness of the samples under forging-low extrusion multistage deformation process were significantly improved compared with that under forging deformation process due to the formation of smaller insoluble particles, finer grains and higher density of matrix precipitates. However, the strength and impact toughness of the samples under forging-extrusion multistage hot deformation process are lower than that under extrusion hot deformation process. The strengthening and fracture mechanisms with different deformation process have been discussed in detailed.     

Thermomechanical ageing (TMA) of 2014 aluminium alloy for aerospace applications

Various thermomechanical ageing (TMA) treatments for 2014 Al-alloy have been developed which include partial peak ageing, warm rolling and further ageing to peak hardness at 160°C. Electron microscopic studies reveal that the TMA treatments affect substantially the ageing characteristics. The TMA-Ib treatment yields finest?′ needles having longitudinal dimensions of ～400 Å. TMA treatment leads to precipitate-dislocation network of different magnitudes. Among the TMA treatments, the TMA IIb treatment results in thickest precipitate-dislocation tangles. In addition to?′, two types of dispersoids Al₄CuMg₅Si₄ and Al₁₂ (Fe, Mn)₃Si have been observed. The density or concentration of these dispersoids is drastically reduced due to TMA treatments. Thus an optimum TMA treatment i.e. TMA-IIb has been developed which results in a significant improvement in the mechanical properties of 2014 Al-alloy.     

Microstructure,tensile properties and fracture behaviour of aluminium alloy 7150

A study has been made to understand the microstructure, tensile properties and fracture characteristics of aluminium alloy 7150. Detailed optical and transmission electron microscopical observations were used to analyse the intrinsic microstructural features of the alloy in the T77 condition. The alloy was deformed to failure over a range of strain rates in environments of 3.5% sodium chloride solution and laboratory air. The environment was found to have little influence on strength of the alloy. The strength only marginally increased with an increase in strain rate. However, for all strain rates, the ductility of the alloy degraded in the aggressive environment. The ratio of strain to failure in sodium chloride solution to that in laboratory air indicates that the alloy is only mildly susceptible to stress corrosion cracking. The fracture behaviour was different in the two environments. However, in a given environment the fracture behaviour was essentially the same. In the aggressive environment fracture was predominantly intergranular while fracture revealed a ductile transgranular failure in laboratory air. An attempt is made to discuss the kinetics of the fracture process in terms of competing mechanistic effects involving intrinsic microstructural features, matrix deformation characteristics, environment and strain rate.     

Influence of aging condition on tensile and fatigue fracture behaviour of aluminium alloy 6063

Abstract

An Al–Mg–Si alloy 6063 was heat treated in the underaged, peak aged, and overaged conditions. The microstructures of the alloy in the different aging conditions were examined using transmission electron microscopy. Tensile and fatigue tests were carried out and the resulting fractures were studied using scanning electron microscopy. It has been found that the alloy shows different tensile and fatigue properties and different modes of fracture under different aging conditions. The results have been explained in terms of slip distribution and grain boundary strength.

MST/1188     

Retrogression and re-aging treatment on short transverse tensile properties of 7010 aluminium alloy extrusions

The influence of retrogression and re-aging treatment (RRA) on short transverse tensile properties of 7010 aluminium alloy extrusions was studied. The short transverse ductility of extrusions, which was much lower in the T6 condition, was improved to the optimum level after retrogression and re-aging treatment. It is found that short transverse ductility is influenced by the nature of precipitate particles located along the grain boundary. It is observed that coarsening of the grain boundary precipitates and its copper enrichment that occurs during RRA are found to be the factors responsible for improvement in stress corrosion cracking (SCC) resistance. The optimum retrogression and re-aging schedule is established that gives rise to the best combination of strength, ductility and SCC resistance.     

铝合金热变形组织演化的模拟

采用基于位错攀移及位错间交互作用的多元位错模型,对Al-Mg-Si(6005)合金热变形过程中亚晶内位错密度,亚晶界位错密度,可运位错位错密度及总的位错密度的演化进行了计算机模拟,并由此对Al-Mg-Si合金热压缩过程中的流变应力演化进行了预报,模拟结果和试验结果吻合较好,采用试验研究的方法建立了亚晶尺寸随变形条件演化的半经验关系模型,为铝合金热变形组织演化的预测和控制提供了实用模型。     

Thermomechanical treatment of 2014 aluminium alloy

Abstract

The effect of thermomechanical treatment on the flow stress, fracture strain, structure, and precipitation behaviour of commercial grade 2014 aluminium alloy has been investigated. Specimens in the supersaturated and aged conditions were plastically deformed in torsion tests in the temperature range 293–493 k and strain rate range 2·8 ×10^?3?2·5 s^?1. It is stated that the starting condition of the alloy acts dominantly on the flow stress, fracture strain, and thermally activated processes, which take place during aging. An increase in temperature results mainly in a reduction of flow stress in the aged alloy and an increase in flow stress in the supersaturated alloy. The supersaturated alloy exhibits negative strain rate sensitivity over the entire range of applied temperature while for the aged alloy it is exhibited only in the temperature range 293–393 K. The effect of temperature and strain rate on the fracture strain of the supersaturated alloy is negligible, but the fracture strain of the aged alloy increases with temperature and decreases with strain rate. In the supersaturated alloy, the process of strain aging is dominant during deformation at room temperature and at higher temperatures precipitation aging and recovery are dominant. In the aged alloy, strain aging is dominant in the temperature range 293–443 K and recovery is dominant only at the highest test temperature (493 K).

MST/616     

Effect of thermal ageing on hardness,tensile and impact properties of an alumina microsphere-reinforced aluminium metal-matrix composite

Thermal ageing studies have been carried out with an alumina microsphere-reinforced 6061 aluminium metal-metrix composite (MMC). A solution treatment temperature of 530°C for 1.5 h and ageing temperature 175°C with ageing time ranging between 0 and 12 h have been used. It was observed that the hardness achieves a peak value in about 8 h; the ultimate tensile strength shows an increase with increasing ageing time, and reaches a plateau at about 10 h. On the other hand, elongation to failure and impact properties show a sharp decline at approximately 4 h of ageing time. Also, a limited amount of experiments using 175°C/8 h ageing after solution treatment at 510, 490, 470 and 430 °C for 1.5 h show that the hardness of the MMC deceases steadily as the solution treatment temperature is decreased.     

Microstructures and tensile properties of commercial purity aluminium alloy AA1235 under different annealing conditions

Microstructures, hardness, tensile properties and texture of cold-rolled AA1235 alloy are investigated under different annealing conditions. Precipitation of Al₃Fe particles occurs during annealing of the alloy. These precipitates largely affect the microstructural behaviour, tensile properties and texture of the alloy. After complete recrystallization no change in mechanical properties is observed upon further annealing.     

Effect of ceramic reinforcement on the ageing behaviour of an aluminium alloy

The effect of a 20vol % alumina microsphere particulate on the age-hardening characteristics of a 6061 Al matrix composite was investigated — based on microhardness, electrical resistivity and X-ray mapping — and the composite is compared to the unreinforced 6061 Al alloy. It is shown that this ceramic reinforcement can affect the age-hardening behaviour of the matrix alloy by significantly accelerating the kinetics of precipitation. This acceleration is related to a decrease in nucleation time and to an increase in the precipitate-growth rate. The relative amounts of age-hardened precipitates are also observed to be affected by reinforcement addition.     

Natural ageing behaviour of cast alumina particle-reinforced 2618 aluminium alloy

The effect of the presence of 10 and 15 vol% alumina particles on the natural ageing behaviour of cast 2618 aluminium alloy was investigated using microhardness measurements and differential scanning calorimetry. It was found that the addition of the alumina particles does not alter the ageing sequence of 2618 AI although certain aspects of the precipitation reactions are changed. In particular, the relative quantities of the various phases were changed by reinforcement addition. Increasing the alumina content decreased the volume fractions of the Guinier-Preston-Bagaryatskii (GPB) I phases. Also, the peak reaction temperature, (T _p), for the GPBII and S phases decreased with increasing volume fraction of alumina.     

Effect of heat treatment on tensile properties of friction stir welded joints of 2219-T6 aluminium alloy

Abstract

The effect of post-weld heat treatment (PWHT) on the tensile properties of friction stir welded (FSW) joints of 2219-T6 aluminium alloy was investigated. The PWHT was carried out at aging temperature of 165°C for 18 h. The mechanical properties of the joints were evaluated using tensile tests. The experimental results indicate that the PWHT significantly influences the tensile properties of the FSW joints. After the heat treatment, the tensile strength of the joints increases and the elongation at fracture of the joints decreases. The maximum tensile strength of the joints is equivalent to 89% of that of the base material. The fracture location characteristics of the heat treated joints are similar to those of the as welded joints. The defect free joints fracture in the heat affected zone on the retreating side and the joints with a void defect fracture in the weld zone on the advancing side. All of the experimental results can be explained by the hardness profiles and welding defects in the joints.     

Influence of thermomechanical aging on fatigue behaviour of 2014 Al-alloy

The fatigue behaviour of 2014 Al-alloy has been studied in various thermomechanically aged conditions. It is observed that fatigue properties can be improved by a thermomechanical treatment, which would reduce the concentrations of dispersoids, provide a relatively uniform deformation structure and produce fine distribution of θ’ precipitates. Fine θ’ particles inhibit dynamic recovery and produce uniform deformation structure, which improves fatigue behaviour. Presence of dispersoids and coarse precipitate particles leads to the formation of persistent slip bands (PSBs) and a highly heterogeneous deformation structure, which cause damage to fatigue properties.     

Rate of workhardening influencing subzero temperature tensile strength properties of heat treated aluminium alloy 7010 plates

Abstract

The tensile properties of aluminium alloy 7010 plates, heat treated to varying aging conditions, i.e. naturally aged, underaged, peak aged and overaged, were examined at ambient and subzero (?50°C) temperatures. It is shown that the maximum increase in strength properties (both 0·2% proof stress and ultimate tensile strength) upon changing the test temperature from ambient to subzero (i.e. ?50°C) is obtained in the case of the naturally aged samples, while there is a minimal increase in the strength properties of the underaged samples when tested at ?50°C. These results are discussed in light of changes in the workhardening behaviour of the materials with aging.     

Subzero tensile properties of vapour quenched aluminium alloys

Supersaturated and metastable aluminium alloy solid solutions containing a dispersed phase have been produced by a vapour quenching technique. Binary alloys contained 3.5% Fe and 5.5% Mn; ternary alloys contained 6 to 9% chromium and 0.5 to 1.2% iron. After rolling into sheet the tensile properties were determined in the temperature range 293 to 77 K. At 77 K tensile strengths of 1115 and 1036 MPa were obtained for two Al-Cr-Fe alloys, equivalent to E/82 and E/83, respectively. These are the highest strengths ever reported for an aluminium alloy. The deformation behaviour at subzero temperatures has indicated the potential for further strengthening of metastable rapidly solidified aluminium alloys by dislocations alone.     

The tensile properties of a superplastic aluminium bronze

The high temperature tensile properties of a micrograin Cu-9.5% Al-4% Fe alloy, which is superplastic at 800° C, have been determined. Elongations at fracture of greater than 700% are achieved when the nominal strain-rate is in the range 3.9×10^–2 min^–1 to 7.9×10^–2 min^–1. The nature of plastic instability in superplastic materials is considered and it is shown that the amount of strain at the onset of plastic instability is inversely related to the applied strain-rate and is relatively independent of the strain-rate sensitivity exponent, m. The onset of plastic instability during a tensile test results in an increase of local strain-rate at the point of minimum cross-section and this, together with the existence of a triaxial stress state in the necked region, may produce errors in the m versus strain-rate plot if m is determined by the change-rate method. The initial strain-rate for maximum elongation is lower than the strain-rate for maximum m. This may be ascribed either to the influence of plastic instability or the formation of cavities at the higher strain-rates.     

Influence of intrinsic and extrinsic factors on mechanical properties of 2090 aluminium alloy weldments

Abstract

Intrinsic and extrinsic factors that influence the mechanical properties of as welded weldments in an Al–Cu–Li alloy, 2090, have been investigated. Electron beam (EB) and gas tungsten arc (GTA) welds were produced in 2090–T3 and 2090–T8. The tensile properties of as welded and solutionised and aged weldments at 293 and 77 K are presented. The results show that differences in thermomechanical processing between the base metal and the fusion zone lead to inhomogeneities in the weldment microstructure and, consequently, differences in properties. In the as welded condition, the EB and GTA fusion zones lack the strengthening precipitates present in the base metal. As a result, increased base metal constraint on the as welded fusion zone confines the plastic deformation to within the weld and therefore the measured mechanical properties of the weldment are those of the weld material. After equivalent thermal processing, the properties of the EB and GTA weldments are as good as, or better than, those of the base metal. In the post-weld solutionised and overaged condition, the base metal lacks the volume fraction and homogeneity of strengthening precipitates found in the EB and GT Afusion zones, and as a result failure occurs in the base metal.

MST/1405